In recent years, an increasing number of handheld (portable) power tools, such as screwdrivers, cutting tools, etc., have been offered with rechargeable battery packs that are attached as the power supply, thereby making the power tool cordless, instead of with power supply cords. In such rechargeable power tools, the battery pack (power supply) has a nominal output voltage that is compatible with the rated voltage of the tool's electric motor (drive source). The battery pack is detachably attached to a tool main body part. Consequently, if the rated voltage of the electric motor is, for example, 36V, then a battery pack having an output voltage of 36V is attached as the power supply. In addition to battery packs having a rated voltage of 36V, battery packs having various other voltages, such as 18V, 14.4V, and 7.2V, have been offered. These battery packs comprise, for example, lithium ion batteries, and a plurality of battery cells is housed in a case; thereby, the battery pack can be reused by detaching it from the tool main body and then charging it using a separately available charger.
US 2008/0035507 discloses a power tool case for storing battery-operated power tools, wherein the case includes a housing, an electrical connector, and an internal electrical outlet. Japanese Laid-open Patent Publication 2011-161603 (and its family member US 2011/0198103) discloses electric power tools powered by a plurality of battery packs that are connected in series.